As it is known, blood pressure is measured by using an instrument which is composed of a pressure gage connected to a cuff with a chamber which can be inflated by means of a bulb, so as to oppose a known pressure to the arterial pressure and therefore allow to read pressure values when blood flow is detected, by listening with a stethoscope during decompression of the cuff and subsequently the level at which the action of the cuff no longer affects the detected sounds.
The inflatable chamber, integrated in the cuff applied to the arm of the patient, produces on the arm a pressure which, at a certain point of the compression, exceeds the arterial pressure, interrupting the blood flow downstream of the cuff.
Once the arterial pressure has been exceeded by 20-30 mm Hg, decompression of the cuff is performed by means of a pneumatic valve integrated in the bulb.
During decompression, the operator listens to the sounds produced by the artery by using a stethoscope which is conveniently placed on the arm. In this manner, the operator detects a series of sounds having different intensities, durations and tones, produced by the arterial pulses, which in turn are generated by cardiac activity and by the resistance of the arterial vessel.
The operator must determine which of these pulses represents the systolic value and which one represents the diastolic value.
However, the procedure described above can be influenced by errors, one of which is that cuffs are usually used which are not proportionate to the circumference of the arm, and this introduces an error which alters the measurement.
In this regard, there is extensive medical literature which agrees in deeming that it is incorrect to use a single cuff regardless of arm size, and in deeming that when the circumference of the arm increases it is necessary to use larger cuffs and, vice versa, arms having a smaller circumference require the use of smaller cuffs. There is unanimous judgment regarding the fact that using the same cuff leads to an overestimation of the values for arms of the former type and an underestimation for arms of the latter type. Although currently there is no unanimous agreement in determining the measurement of the error that is introduced, it is found that this error is certainly substantial and such as to induce, in many cases of people with arms having a larger circumference, the prescription of an antihypertension therapy which is harmful for the patient and expensive for the public, or an underestimation of hypertension of patients with a small arm circumference.
On the other hand, the use of several cuffs is, from the point of view of medical practice, a solution which is difficult to provide, due to the consequent need of the doctor to have and carry with him a bulky set of various cuffs and due to the increase in the time required to measure the pressure, since in each instance it is necessary to measure the circumference of the arm and then apply the most suitable cuff.
Moreover, the correction could not be absolute, since it is evidently not possible to have a set of cuffs of so many sizes as to ensure the same measurement precision for each arm diameter.